1. Field of the Invention
The invention relates to a smelting apparatus including an electrolytic cell used in the electrolysis of a metal compound to produce the metal, and more particularly to a hoist apparatus for positioning an anode relative to a cathode to achieve a desired predetermined anode-cathode gap.
2. Reference to Prior Art
The electrolysis of alumina (Al.sub.2 O.sub.3) to produce aluminum is a well known process involving an electrochemical oxidation-reduction reaction. A smelter used in this process includes an electrolytic cell including a plurality of anodes and a pot which contains an electrolyte and which functions as a cathode. The anodes are immersed in the electrolyte and are positioned above the floor of the pot to provide an anode-cathode separation distance or "air" gap. An electrical current passes between the anodes and the cathode and through the electrolyte such that the aluminum constituent of the alumina is reduced together with a corresponding oxidation reaction.
For efficient operation of the electrolytic cell, the anode-cathode gap should be set and maintained at a predetermined optimum distance. For example, a potentially significant voltage drop can occur between the electrodes if the anode-cathode gap is too large, and short circuiting of the electrodes or re-oxidation of reduced aluminum can occur if the anode-cathode gap is too small. A gap distance that lies outside of an optimum range produces erratic heating and power loss and reduces anode life.
After the anode-cathode gap is initially set, it must be monitored and periodically reset to ensure proper anode positioning. For example, conventional carbon anodes are consumed over time and individual anodes can be consumed at different rates making resetting to account for changes in anode height necessary. Also, the floor of the pot can become uneven or warped over time and individual anodes must be set accordingly to achieve the desired spacing.
In a known process for adjusting anode position, workers manually raise and lower an anode with reference to paint lines placed on the anode stem. After checking the resistance at the bus bar, the position of the anode is adjusted, using the paint lines as a reference. This is repeated until a resistance value generally indicative of a satisfactory anode-cathode gap is obtained. This process is time consuming, requires the workers to remain in the unpleasant environment of the smelting furnace, and brings the workers into close proximity with the smelting furnace.